1. Field
The disclosed concept pertains generally to photovoltaic panels or arrays and, more particularly, to protection devices and systems therefor. The disclosed concept further pertains to photovoltaic systems.
2. Background Information
Power sources that generate electrical energy usually contain a mechanism to shut off the source of power when the electrical energy is no longer needed, or if there is danger of causing harm to people or equipment.
For example, an electromechanical generator has a prime source of power, such as a gas or diesel engine. In an emergency condition, the source of fuel can be turned off (e.g., by a valve) or the engine can disconnected from the generator, thereby allowing the generator to spin down, stop and cease producing energy.
For alternative energy sources, such as windmills having turbines or wind turbines to generate energy, the turbine can be disconnected from the rotor blades moving the turbine in order to stop the generation of energy. Alternatively, the rotor blades can be rotated to stop the creation of lift on the rotor blades and cause them to stop spinning, thereby stopping the turbine from spinning and creating electrical energy.
U.S. Patent Application Publication No. 2011/0172842 discloses the use of switches to shut down an attached solar module. The switches can be mechanical switches, semiconductor-type switches, such as MOSFET transistors or other similar switches, or any suitable type of switch.
U.S. Patent Application Publication No. 2010/0071744 discloses a photovoltaic (PV) installation including a PV array, an electrical interface connecting a utility power source to an electrical load, and a DC to AC inverter. A first set of wiring electrically connects the PV array to the inverter through a disconnect device and a second set of wiring electrically connects the inverter to the electrical interface. A control mechanism connects the disconnect device to the electrical interface, in order that when power from the electrical interface is removed, the PV array is electrically disconnected from the inverter. The disconnect device may be a remote disconnect device located at a position at or near the PV array, such as in the space beneath a roof supporting the PV array.
However, these proposals do not prevent photovoltaic cells from providing a potential voltage that could feed a fault between a photovoltaic panel and a first switch or disconnect device. As a result, there is an area where there is no protection. As long as the sun or another source of light is shinning on the photovoltaic or solar cells, they produce electrical energy. This is more evident when there are relatively many cells in an area and relatively long runs of cabling combine the cells to create higher voltages and/or larger current capabilities. There have been recent instances of such cells creating fires because of loose wiring or short circuits. There is also an electrocution danger to first responders to a location with cells generating electrical energy because the responders cannot completely turn off the cells.
FIG. 1 shows a photovoltaic generation and distribution system including a plurality of photovoltaic or solar cells 1, distribution wire 2, a first DC disconnect or circuit breaker 3, an inverter 4 for converting DC voltage to an AC voltage, a grid interconnection circuit breaker 5, and an electrical grid or a number of electrical loads 6. A zone of no protection 7 exists when the cells 1 are generating electrical energy. The zone of no protection 7 is where the cells 1 can produce unwanted electricity at a time when, for example, workers, firemen or first responders to an emergency are in the area. This zone of no protection 7 is also prone to relatively high current faults, arcing faults and ground faults.
FIG. 2 shows another photovoltaic generation and distribution system that is somewhat similar to the system of FIG. 1, except that it is larger, includes more photovoltaic or solar cells 1 and more distribution wire 2 to combine the multiple cells. Hence, the corresponding zone of no protection 7′ has expanded with more distribution wiring and with multiple photovoltaic panels including the cells 1.
U.S. Patent Application Publication No. 2012/0174961 discloses a photovoltaic system including one or more solar panels, and one or more shuttering assemblies, each of which is configured to selectively limit the quantity of light received by one or more of the solar panels. A control module is configured to direct the one or more shuttering assemblies to reduce the quantity of light received by at least one of the one or more solar panels in response to signals indicating there is an arc fault event in the photovoltaic system. The shuttering assembly includes an elongated, opaque sheet that is biased into a wound or stowed position. The sheet is movable via a motor from the stowed position to an unwound or blocking position in which the elongated sheet extends across and substantially covers the light-receiving surface of the string of solar panels.
There is room for improvement in photovoltaic panels and arrays.
There is also room for improvement in photovoltaic systems.